1. Field of the Invention
The present invention relates to an infrared blocking optical semiconductor device.
2. Description of the Related Art
In recent years, the number of apparatus having an optical semiconductor device such as an optical sensor mounted thereon is increasing. From an ecological point of view not only small-sized portable apparatus such as a cellular phone and a smart phone but also a flat screen television, a refrigerator, an air conditioner, a lighting fixture, and the like, which are so-called home appliances, carry an optical sensor mounted thereon. Such optical sensors specifically include a proximity sensor for detecting approach of a human body, an illuminance sensor for detecting brightness of the outside to presume absence of a person in a house, and an illuminance sensor for, similarly, detecting brightness of the outside to adjust an amount of light emitted from a backlight or a lighting fixture.
The development of the home appliances such as a flat screen television faces challenges of improving the performance thereof year after year, and, in addition, increasing an energy saving rate, and many of the home appliances have the function of finely controlling illuminance. Electronic components used in such portable terminals and home appliances are, as more functionality and portability thereof are sought, required to be more miniaturized, thinner, more power saving, and reduced in cost. As a result, resin molded packages appear to be often adopted. As a background thereto, there is a trend toward commonality of components and materials. An optical semiconductor device which is one of electronic components mounted for reducing power consumption is no exception, and, similarly to other electronic components, many of optical semiconductor devices are more miniaturized, thinner, and reduced in cost using a resin molded package.
FIG. 8 is an exemplary disclosure of an optical semiconductor device in which an optical semiconductor element 3 is mounted on a resin molded lead frame substrate 2 (for example, FIG. 2 of Japanese Published Patent Application No. 2005-191498). In this case, the resin molded lead frame substrate is a resin molded package in which a lead frame is encapsulated in advance in a resin except for an upper surface of an element mounting portion and there is a hollow portion over a surface to be the element mounting portion. Connections are made via gold wires 4 to the optical semiconductor element 3 mounted on the bottom of the hollow portion, and a hermetic seal is made with a cover glass 7 which transmits light.
Depending on the application of the illuminance sensor, there are cases in which a silicon photodiode is used as the optical semiconductor element 3. A silicon photodiode has spectral sensitivity to an infrared region. FIG. 4 shows exemplary spectral sensitivity of the silicon photodiode. FIG. 5 shows human luminosity. The silicon photodiode has sensitivity over a wide infrared wavelength region, and thus, in order to conform the spectral sensitivity of the silicon photodiode to human luminosity, an infrared blocking filter is necessary. FIG. 9 illustrates an exemplary disclosed structure of an optical semiconductor device in which an infrared blocking filter 11 is placed over the silicon photodiode to conform the spectral sensitivity of the optical semiconductor device to human luminosity (for example, page 5 and FIGS. 1 and 3 of Japanese Published Patent Application No. 2011-060788). The optical semiconductor element 3 is connected to a glass epoxy resin substrate 8 via the gold wire 4, a visible-light and infrared blocking resin 10 and a visible-light resin 9 are molded, and the infrared blocking filter 11 is placed.
Among cases in which the infrared blocking filter is formed by mixing infrared absorbing particles, there is an example in which particle diameters of particles used as the infrared blocking filter are adjusted to disclose an optimum particle diameter for use as a filter (for example, page 15 of Japanese Published Patent Application No. 2011-065146). When the particle diameter is similar to a wavelength of infrared radiation to be absorbed, the infrared radiation is scattered by Mie scattering. When the particle diameter is smaller than the wavelength of the infrared radiation, transition is made from a Mie scattering region to a Rayleigh scattering region. It is disclosed that Rayleigh scattering reduces inversely with the sixth power of an average particle diameter, and thus, the amount of scattered light is very small when the particle diameter is sufficiently small, preferably when the average particle diameter is 100 nm or less.
In general, as the infrared blocking filter, phosphate-based glass doped with copper ions or interference filter glass having a multilayer film formed thereon is used. FIG. 6 shows exemplary spectral characteristics of the phosphate-based glass doped with copper ions. FIG. 7 shows spectral characteristics of the interference filter glass using a multilayer film. Phosphate-based glass doped with copper ions is an infrared blocking filter of a type which absorbs infrared radiation and has a feature in that the spectral characteristics thereof does not change even if an incident light angle changes, but there is a problem in that the infrared blocking filter is inferior in resistance to moisture. Interference filter glass is an infrared blocking filter of a type which reflects infrared radiation and has a feature of having satisfactory resistance to moisture, but there is a problem in that, when an incident light angle changes, an optical path in an interference film through which incident light passes changes, and thus, the spectral characteristics of the infrared blocking filter changes. As shown in FIG. 7, the spectral characteristics with regard to vertical incident light are similar to luminosity characteristics, but the spectral characteristics with regard to oblique incident light deviate from the luminosity characteristics, and transmitted light is observed also around 750 nm. There are cases in which an infrared blocking filter formed by mixing infrared absorbing particles uses infrared absorbing particles that are smaller than the wavelength of the infrared radiation, i.e., 100 nm or less. However, there is a problem in that, as the particle diameter becomes smaller, reduction in size of the particles becomes tremendously difficult, which requires additional costs, facilities, and time for the reduction in size.